Non-destructive testing is used in numerous areas of endeavor. One form of non-destructive testing uses sound waves or pulses, generally in the ultrasonic region of the spectrum. In a typical instance, an outgoing pulse (or stimulus) is produced incident to a structure under analysis. Echoes resulting from the pulse are then recorded and analyzed in order to determine structural layering, topography, defects and other characteristics.
Generally, it is necessary to use ultrasonic pulses (stimuli) having wavelengths shorter than the layer thicknesses of the material being tested in order to accurately analyze the resulting echoes. However, shorter ultrasonic wavelengths do not penetrate laminate materials to the same depths as do longer wavelengths. Therefore, improved techniques and equipment for ultrasonic testing of laminate materials using longer ultrasonic wavelengths would have desirable utility.